They're in the konbinis.

Technically you're supposed to wait around and consume your product at the shop where you've bought it, but I didn't have any objections to doing one-in one-out, so as long as I bought a new drink I just dropped the refuse from the last one at the store where I bought the next one.

and yet there’s no trash and the streets are clean.

Patently not true - there are rubbish bins and recycling bins all over the place in Japan.